notes/IT/Scripting.md

Marking a script as executable

Sometimes, you may need to mark a script as an executable to run it. On Linux, this can be accomplished by chmod +x [FILE], where [FILE] is the file you want to mark as executable. To unmark a file as executable, use chmod -x

The Shebang

There are various shells with their own language syntax (sh, bash, fish, etc). Therefore, more complicated scripts will indicate a particular shell by specifying the absolute path to the interpreter as the first line, prefixed by #! like this:

#!/bin/sh
echo "Hello, World!"

#!/bin/sh means that this script can be executed by the binary located at /bin/sh, and so the reader knows this is a sh(ell) script.

Variables

In bash, variable assignment is done with the = operator. Variables are conventionally named with SCREAMING_SNAKE_CASE, and can be accessed by prefixing the variable name with a dollar sign ($):

#!/bin/bash
# There may not be any spaces used during assignment, `A = B` means something different than `A=B`
# Assignment is done with the equal sign (=) operator:
MY_VARIABLE="Hi Mom!"
echo $MY_VARIABLE

Quotes

In Bash, different styles of quotes mean different things:

Quote	Description

Commands

Command	Description
exit [CODE]	Make the script process exit, where [CODE] is the exit code the process will terminate with.